Process for producing alkali metal sulphides



Jan. 7, 1941. E. LANzl-:TTI

PROCESS FOR-PRODUCING ALKALI METAL SULPHIDES Filed April 15, 1956 NolENFZmUZoU mmmvIU @23000 INVENTOR. ENzo LANZETT/ zar-.3.6m m NM2 www:

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Patented Jau. 1', 1941 UNITED STATES PATENT OFFICE 2,227,547 PROCESS FOBPBODUUING ALKALI METAL SULPHIDES Enzo Lanzettl, Como, Italy, asslgnor toLuigi Achille, Milan, Italy Application April 15, 1936, Serial No.74,592 In Italy June 15, 1935 5Claims.

lution of the corresponding alkalimetal polysul- According to thisinvention, the sodium sulphide, which usually is prepared by reductiono! the sodium sulphate with carbon, is produced by reaction of sodiumamalgam with aqueous solu tion of sodium polysulphide or a solution oisulphur in aqueous sodium sulphide.

The polysulphide may be prepared by reaction of sodium sulphide withsulphur and then reacted with the amalgam, or the solution of thesulphur in the sodium sulphide and the reaction with the amalgam arecaused to take place at the same time,

The reaction forming the basis oi the process may be represented asiollows: l

uundamentally the invention thereiore resides in the synthesis ci thesodium sulphide from sodium in lthe amulgam and elemental sulphur.

it is obvious that when the amount ci allrall-l ncetal ci the amalgamdoes not correspond to that oi the polysulphide used, sulphides areobtained.

Example i @ne oi the Well-known electrolyaers provided with a poromdiaphrauui may he employed, the electrolyte hein@ a concentratedsolution oi common salt.. `lliurinu the electrolysis duely dividedsulphur is brouuht to contact with the electrolyte consisting ol sodiumamalgam iu the cathodic chamber only. The liquid in the cathodic chamhermay be agitated by suitable means. During the operation the addition oi.the sulphur is controlled in auch a way that the total sulphur content(S :including Naas) in the electrolyte of the cathodic sone ismaintained in such a. manner that for the electric conductivitysubstantially the NaCl is decisive. 'I'he apparatus may he heated orcooled by suitable means. When continuing the electrolysis Nage isformed in the cathodic zone by the combination of the nascent alkalimetal with sulphur, for instance, in the iorm of NanSc. The electrolyticreaction may be represented by the following formula:

smell-sendmail mixtures ol allrali metal It may be assumed that ondaryreaction takes place:

From. the solutions containing sodium sulphide 5 and sodium chloride orin some cases sodium sulphide, sodium chloride and sodium hydroxide, thesodium sulphide may be separate by one of the Well-known methods. Theprocess as described may also be carried out continuously by 10correspondingly controlling the current intensity as well as the supplyof the electrolyte and the sulphur.

the following sec- Emamplc 2 The apparatus used may be an electrolyserl5 provided with bell or an electrolyzer provided With a liquid diaphmThe electrolyte may he a concentrated solution ol potassium chloride.During the electrolysis the electrolyte is brought in. the cathodic zoneto contact with Kelis dis- 2u solved, lor instance, in water. During theoporm ation the addition oi Kaus is controlled in such a way that thetotal sulphur concentration (S4-Else) in the electrolyte of the cathodiesone is kept within such limits, that the KCl is decisive 25 for theelectric conductivity.

The apparatus may be heated or cooled. Un contiuuinc the electrolysisits@ ls obtained in the cathodlc zone by the combination of E 'withKea..

The electrolytic reaction may loe eitpressed as mucus:

fenomenos-amapola llhe iollowlng secondary reaction is assumed to tolteplace:

,The process may be carried throuph continuously as in Eixample l. Thepotassium sulphide :may be separated trom the resulting solutions t@ byone oi the well-known methods.

Esempio :i

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pended in a suitable medium, for instance, water, NazS is formed by thereaction between the amalgam and the sulphur according to the followingformula:

2Hg'Na+s- Na2s+2ng The following secondary reaction may take place:

Hg+S=Hes Furthermore the following reaction might oc- The contactbetween the amalgam and the sulphur may take place in the state ofstatic equilibrium or may be intensified by stirring. The apparatus maybe heated or cooled as required. The sodium sulphide may be separatedfrom the solution or suspension by well-known methods. The process mayalso be carried through continuously.

Example 4 The decomposition of the amalgam may be effected in a separateapparatus. The latter may be of different type or shape (tube, channelor chamber) and may consist of metal or other suitable material. It maybe provided with agitating means or not, and may further be providedwith means for heating or cooling. The amalgam which is introduced intothe apparatus continuously or intermittently may be of differentconcentration, for instance, it may contain 5 grams Na per 1000 gramsHg. The amalgam is brought to contact in the reaction apparatus with anaqueous solution of NazSz, the operation being controlled in such a waythat during the contact between Hg and NazSz also HgNa is continuouslypresent. In other terms the reaction takes place in continuous presenceof HgNa., for instance, 0.6 gram of Na being present per 1000 grams ofmercury. Inthis way I may attain that not HgS but NazS is formed by thecombination of the amalgam with the polysulphide. The reaction may alsoproceed according to the following formulae:

HgNax-i-NazSz-NaeS-l-HgNa-z or, as the case may be,

Hg Nas 2+2Hg-Na=3Hg+2Na2s The following secondary reaction may occur:

HgNax-i-HzOeNaOH-i-H-{FHgNai-i The resulting amalgam may be returned,either immediately or after the remaining sodium has been removed bywell-known methods, to circulate again in the electrolytic apparatus.

The process may also be carried out continuously. The sodium sulphidemay be separated from the solution by well-known methods.

Example 5 The same apparatus as mentioned sub 4 may be employed. Thesodium amalgam is brought to contact in the reaction apparatus, forinstance, with an aqueous alcoholic solution of NazSs, care being takenthat during the contact between the amalgam and the solution alwaysactivated S(Na2S1) be continuously present. In this case I may avoid theformation of NaOH, only NazS being formed. The reaction may be expressedby the following equation:

As a secondary reaction the formation of HgS may take place according tothe well-known formula. The process may be a continuous one.

Example 6 The same apparatus is employed as sub 4. In the reactionapparatus the sodium amalgam comes into contact, for instance, with anaqueous solution of Na2S4. The process is conducted in such a way thatboth the conditions of Examples 4 and 5 are realized, i. e. the contactbetween the amalgam and the Na2S4 is accomplished in such a. manner thatsodium and activated sulphur are always present.

Furthermore the process is conducted in such a way that during thecontact stoichiometric ratios exist between the amalgam and the Na2S4 toobtain a sodium sulphide of greatest purity.

By proceeding in this way the formation of NaOH and HgS may be avoidedand a sodium sulphide of excellent purity may be obtained. This processtoo may be carried out continuously; the sodium sulphide may beseparated by crystallisation or fusion. l

To avoid the formation of mercury sulphide during the reaction, theamalgam should be slightly in excess. 'Ihe mercury sulphide is solublein solution of sodium sulphide with formation of Hg(NaS) 2, which,through the action of the amalgam, gives NazS and Hg, according to theequation:

In order to avoid the formation of sodium hydroxide, it is suitable toexclude materials tending to cause decomposition of the amalgam.

Generally the reaction between amalgam and polysulphide to form thesodium sulphide is aided by thorough contact among the reagents, byincrease in the temperature, by increase of the quantity of sodium inthe amalgam and by increase of the sulphur content in the polysulphide.

Upon the accompanying drawing is shown dlagrammatically, the apparatuswhich may be utilized. The electrolytic cell l may be used for theproduction of the amalgam while the sodium poly-sulphide may be producedin the chamber 5.

The sodium amalgam and sodium polysulphide are then caused to flowtogether into the reaction apparatus 2.

In the reaction chamber 2, the characteristic orange color of thepolysulphide solution will be decolorized progressively as thepolysulphide is converted to the sulphide.

A part of the sodium sulphide solution obtained is passed into thechamber 4 where sulphur is added to it and it is then passed into thechamber 5 for reintroduction into the chamber 2.

The remaining portion of the sodium sulphide may be passed into thecooler 6 for the preparation of crystals containing 32% NazS or into aconcentrator 1 where sodium sulphide is provided having a concentrationof 62% NazS.

The mercury from the reaction apparatus 2 is washed in the apparatus 3and then returned to the electrolytic cell I.

I claim:

1. The process of producing alkali metal sulphides which comprisesreacting an alkali metal amalgam with an aqueous solution of thecorresponding alkali metal polysulphide.

2. The process of producing alkali metal sulphdes which comprisesreacting an alkali metal amalgam with an aqueous solution of thecorresponding alkali metal sulphide and sulphur.

5. In the manufacture of sodium sulphide, the improvement whichcomprises reacting sodium amalgam with the corresponding sulphide andsulphur in an aqueous medium to form additional sodium sulphide.

ENZO LANZETTI.

